hand in a fist slowly moving from your chin outwards

We do it slowly because it's a long vowel and we level our hands with our mouth to better connect lips and hands movements.

Make a fist with your hand to show that this vowel is very rounded. Rest one side of your fist on your chin, and then slowly pull it forwards, meaning that (in modern pronunciation) the lips go forwards, producing a sound which is a mixture of Latin I and U (much like the French sound of the letter U, as in "future").